In his official announcement on Thursday, Menino assured his supporters he would not disappear.

"I'm not retiring, just turning one page on this chapter to the next," he said.

Earlier in the day at City Hall, councilors praised him, acknowledging that the "time has come" for the changing city, but agreeing it is a bittersweet day.

"It’s a changing city and it’s a changing day. The whole guard is going to change around here," Councilor Stephen Murphy said.

"It’s a sad day. I think we celebrate all the things this man has done to make this city better. It’s a safer city; it’s built up in a different way; it’s a more fun city," Councilor Tito Jackson said.

Councilor Felix Arroyo said he, like many in the city, was shocked and surprised by the decision.

"He’s been the mayor since I was 14 years old," Arroyo said. "We were all taught to leave this place better, and he could do that and see it in a tangible way. He’s living the dream."

"I’m thinking about all of his visionary leadership, his tireless work ethic, his humility always reminding us to put people at the forefront of every decision that we make," said Councilor Ayanna Pressley.

New York City Mayor Michael Bloomberg lauded Menino for his work in trying to reduce gun violence in urban neighborhoods.

Menino and Bloomberg served as co-chairs of Mayors Against Illegal Guns.

Democratic congressman Stephen Lynch of South Boston, who is running for the U.S. Senate, said Menino helped lead a transformation in the city over the past 20 years and will be considered one of its greatest mayors.

Interim U.S. Sen. William "Mo" Cowan said Menino was a champion for fairness and equality for all residents.

The praise for Menino was not limited to his political colleagues. Residents, too, said they will miss the mayor.

Shirley Clarke, whose 13-year-old son, Gabriel, was shot in Dorchester on the way to choir practice, says Menino reached out to her family in their time of need.

"Our situation was desperate and overwhelming, and the way the mayor reached out personally to my family and embraced us … he made a promise and kept them," she said.

"For more than two decades, Mayor Menino has served the city and every one of its residents with extraordinary leadership, vision, and compassion. His efforts to revitalize neighborhoods, schools, and businesses, better integrate police officers into their communities and reduce gun violence, reach out to the homeless and marginalized, and engage young people in the life of their city has charted Boston on a course for a better future," President Barack Obama said in a statement. "No two people wear their hearts on their sleeve for the City of Boston and its people as openly as Tom and Angela Menino."